In satellite communication systems, a signal is transmitted between a feeder earth station by means of an uplink to the satellite. The satellite receives the signal, amplifies it and then re-transmits the signal to a service area of the earth's surface by means of a downlink.
Current satellite transmission systems include fixed gain amplifiers with their operating points determined during the design of the communication system to achieve predetermined system performance goals. The transmission systems are designed at their inception with sufficient transmit power to overcome a low probability precipitation event which may otherwise have an adverse effect on signal reception at a particular location within the coverage area of the satellite. For example, a system requiring 99.9% link availability with an accompanying signal loss due to rain in the transmission path will be designed with additional satellite radio frequency (R.F.) transmit power applied to the given downlink antenna beam in order to overcome the effects of the rain. In other words, an availability due to rain of 99.9% defines a fixed margin (measured in decibels) which will not be exceeded more than 0.1% of the time. The fixed margin consists of rain attenuation and in the case of the downlink, an increase in subscriber antenna temperature due to the attenuation. The required fixed margin depends on the local rain rate and, in the case of the downlink, the elevation of the subscriber's antenna, and can vary significantly over the service area. The effects of differences in slant range between the satellite and subscribers also can be taken into account. This R.F. transmit power is constant and cannot be adjusted over the lifetime of the satellite. Furthermore, the transmit power is applied to an antenna beam covering the entire service area. Consequently, satellite power requirements are oversized to achieve the desired link availability and customer satisfaction during anticipated weather conditions. This sizing and utilization of R.F. transmit power is inefficient, particularly where the satellite has a broad coverage area. In general, the cost of a satellite is related to its power rating.
One approach to solving this problem has been to produce a complicated satellite transmission system utilizing many spot beams each of which are adjusted in power level in response to real time weather data for each spot beam. For example, see U.S. Pat. Nos. 6,421,528 B1—Rosen et al. and 6,799,014 B2—Rosen et al. Such a system requires many spot beams and much hardware to accommodate the instantaneous adjustment of the power for each spot beam. This is an inherently large complex system requiring much hardware which is prone to having a lower reliability rating. For example, intense rainfall is characteristic of thunder storms which are typically several miles in extent. The beam elements out of which the pattern would be formed would need to be several miles in extent in order to “track” the rain cells. This may require an antenna on the order of 10 to 15 meters with 500 to 1000 beam elements and a corresponding number of beam forming elements. Considering the power, weight and cost of such an implementation, an improvement is needed in this area.